Bis[2,3-bis(thiophen-2-yl)pyrido[3,4-b]pyrazine]silver(I) perchlorate methanol disolvate

The structure of bis[2,3-bis(thiophen-2-yl)pyrido[3,4-b]pyrazine]silver(I) perchlorate methanol disolvate is monoclinic. The Ag atom coordinates pyrido N atoms and is two-coordinate; however, the Ag atom has nearby O atoms that can be assumed to be weakly bonding – one from the perchlorate anion and one from the methanol solvate. One of the thienyl groups of a 2,3-bis(thiophen-2-yl)pyrido[3,4-b]pyrazine is flipped disordered and was refined to occupancies of 68.4 (6) and 31.6 (6)%.

The title compound, [Ag(C 15 H 9 N 3 S 2 ) 2 ]ClO 4 •2CH 3 OH, is monoclinic.The Ag I atom is coordinated by pyrido N atoms and is two-coordinate; however, the Ag I atom has nearby O atoms that can be assumed to be weakly bonded -one from the perchlorate anion and one from the methanol solvate molecule.One of the thienyl groups on a 2,3-bis(thiophen-2-yl)pyrido [3,4-b]pyrazine is flipped disordered and was refined to occupancies of 68.4 ( 6) and 31.6 (6)%.
The bis complex with silver utilizes the pyrido N atom in the pyrido [3,4-b]pyrazine to make a nearly linear, nearly flat silver(I) complex where the N-Ag-N angle is 175.25 (14) � .This is interesting compared to bis complexes with 2,3-diarylquinoxalines which have no choice but to bond to metals using the quinoxaline N atoms, which are more sterically hindered due to their close proximity to the aryl groups on neighboring C atoms.Additionally, the Ag I atom is weakly coordinated by two O atoms -a methanol O atom (O6, Fig. 1) at 2.782 (4) A ˚and a perchlorate O atom (O1) at 3.079 (5) A ˚, thereby mimicking a four-coordinate square-planar environment (Table 1).
Like many bis 2,3-dithienylquinoxaline complexes with metals where one thienyl ring is nearly coplanar with the quinoxaline ring (Crundwell & Ellis, 2023), here also one thienyl ring in each ligand is nearly planar with the main pyridopyrazine moiety.Based on least-squares-plane calculations, the thienyl rings containing S1 and S3 (Fig. 1) make angles of 11.2 (2) and 4.35 (11) � , respectively, with respect to the least-squares-plane determinations of the pyridopyrazine atoms.By comparison, the thienyl rings containing the S2 and S4 atoms make angles of 50.36 (11) and 64.5 (5) � .Also typical for these thienyl rings are flip disorders.The thienyl ring containing the S4 atom exhibits a flip disorder of 68.4 (6)/ 31.6 (6)%.
Finally, there are several hydrogen bonds in the structure (Table 2).The most significant hydrogen bonds involve the hydroxy groups on the two methanol solvent molecules.The methanol O atom (O6, Fig. 1) that weakly coordinates to the Ag I atom also has a H atom that is hydrogen bonded to the neighboring methanol (O5), which, in turn, particpates in a hydrogen bond by donating its H atom to a symmetry-related perchlorate anion.
A 30 ml methanol solution of 148 mg (0.50 mmol) of pyridopyrazine was stirred and warmed until the ligand dissolved.A 5 ml solution of 52 mg (0.25 mmol) of silver perchlorate in methanol was added to the former solution.The resulting mixture was removed from heat and transferred into test tubes that were individually placed into amber vials.The amber vials were loosely capped and were placed in a drawer to remove them from ambient room lighting.Diffractionquality pale-yellow plates formed via slow evaporation of the solvent within 48 h.Crystals were harvested from the evaporating solutions.Crystals slowly desolvated upon standing in open air and were thus covered in paraffin oil for data collection.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 3.
A ring-flip disorder of 68.4 ( 6) to 31.6 (6)% was determined for one of the ligand thienyl rings.This disorder was treated by a FLAT restraint to the flipped component atoms of the thienyl ring along with SADI and SIMU restraints to control data reports     bond lengths and displacement parameters, respectively.The displacement parameter of the C atom that connects the thienyl ring to the pyridopyrazine ring was constrained to be idenical in both flipped orientations using an EADP constraint.
Finally, an H atom on a methanol solvent molecule was restrained such that it made a hydrogen bond with a neighboring methanol.

Special details
Geometry.All esds (except the esd in the dihedral angle between two l.s.planes) are estimated using the full covariance matrix.The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry.An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s.planes.Refinement.H atoms on sp 2 and sp 3 C atom were placed at calculated positions with C-H distances of 0.93 and 0.96 Å and were included in the refinement in riding-motion approximation, with U iso (H) = 1.2U eq or 1.5U eq of the carrier atom, respectively.Hydroxy-group H atoms were also placed at calculated positions with an O-H distance of 0.82 Å and were included in the refinement in riding-motion approximation, with 1.5U eq of the carrier atom.

Figure 1 A
Figure 1A view of the title compound.Displacement ellipsoids are drawn at the 50% probability level.The dotted bonds illustrate the nearby O atoms from a methanol and from the counter-anion.All H atoms have been omitted, as has the minor component of the disordered thienyl ring.

Table 3
Experimental details.